1. Field of the Invention
This invention relates to a medical assembly. More particularly, this invention relates to a stent-catheter assembly with a releasable connection that enhances stent retention during delivery of the stent and methods of constructing such an assembly.
2. Description of the State of the Art
A stent is a device that holds tissue in place and is often used to support tissues while healing takes place. A stent can keep “tube-shaped” structures such as, for example, blood vessels, open after surgery. Stents may also be used, for example, in creating an arterio-venous fistula in a hemodialysis patient, reattaching intestines after a temporary colostomy, and keeping a ureter open after surgical removal of a blockage in the ureter. Typically, stents can be compressed to a reduced diameter, inserted through small lumens with catheters and expanded to a larger diameter when positioned at a desired location. Examples of stents in the patent literature include U.S. Pat. Nos. 4,733,665, 4,800,882, and 4,886,062.
In the early 1990s, physicians began using stents to improve angioplasty procedures. An intraluminal coronary artery stent can be a small, self-expanding or expandable, stainless steel mesh tube that is placed within a coronary artery to keep a grafted vessel open during a coronary artery bypass graft surgery or after balloon angioplasty to prevent restenosis of the vessel.
In a typical percutaneous transluminal coronary angioplasty (PTCA) procedure, a guiding catheter is inserted percutaneously through a brachial or femoral artery and advanced through the vasculature until the distal end of the guiding catheter is in a desired position within a lumen of a coronary artery. A guidewire and a dilatation catheter having a balloon on the distal end are introduced through the guiding catheter. The guidewire is advanced into the patient's coronary vasculature, and the dilatation catheter is advanced over the guide wire until the balloon is properly positioned in the lumen of the artery across an arterial lesion such as, for example, a lesion of atherosclerotic plaque or a calcified lesion.
The balloon is inflated to a predetermined size with a radiopaque liquid at a relatively high pressure to radially compress the lesion and remodel the lumen of the artery. The balloon is deflated, the dilatation catheter is withdrawn from the patient, and the blood flow is resumed through the dilated artery. To avoid restenosis, an intravascular stent can be implanted to maintain vascular patency. The stent is typically transported through the patient's vasculature on the balloon portion of a catheter.
A problem with current stent-catheter assemblies is that the stent may become detached during the process of positioning the stent in a patient's vasculature. The combination of the stent and dilatation catheter must have a small, delivery diameter and, the stent must be firmly attached to the catheter to avoid detachment of the stent before it is properly positioned in the lumen of the vasculature.
Crimping is currently used to attach stents to dilatation catheters and may fail. This failure is problematic, since loss of the stent during positioning can result in medical complications. A lost stent is, in effect, an embolus that can create a thrombosis and require surgical intervention. One approach to solving the problem of lost stents has been to attach stents to balloons with a pressure sensitive adhesive, which simply anchors the stent on the balloon. Unfortunately, pressure sensitive adhesives have created additional problems. One problem is that the stent may be damaged or displaced upon deflation of the balloon. Another problem is that residual adhesive may be physically moved to the stent's inner surface upon deflation of the balloon, where the adhesive can affect the movement of other catheters and guidewires through the stent, as well as the biocompatibility of the stent.
Another approach to solving the problem of lost stents has been to attach stents to balloons with a photodegradable adhesive. The photodegradable adhesive is degraded by directing light to the adhesive after proper positioning and delivery of the stent. Unfortunately, photodegradable adhesives require including optical fiber in the stent-catheter assembly, which increases both the cost and physical size of the assembly—two factors that are unappealing to a cardiovascular surgeon.
Accordingly, one of skill in the art would benefit from a stent-catheter assembly having a connection that retains the stent for proper delivery and placement, releases the stent without damaging or displacing the stent from its desired location, does not reduce biocompatibility, and is appealing to one of skill in the art due to any combination of a variety of factors including, but not limited to, ease of use, biocompatibility, therapeutic and prophylactic benefit to the patient, and cost.